Restoration of forests supports the conservation of pollinators in intensively managed agricultural landscapes

Many intensively managed agricultural landscapes of Europe are extremely poor in forests, which are among fundamental habitats for pollinating insects. To compensate for ongoing forest loss, compensatory afforestation is being widely implemented, especially in deforested areas, although empirical knowledge about its effectiveness for biodiversity conservation is still scarce. Here, we aimed at exploring the potential of biodiversity offsetting through restoration of forests in supporting pollinators in temperate agricultural landscapes. We compared understory pollinator communities between 17 lowland oak-hornbeam restored forest patches older than 20 years with those observed in 17 natural forest remnants, referenced here as the target habitat of ecological restoration. Species richness, abundance, and evenness of bees and hoverflies did not differ between restored and remnant forests, while we observed a lower abundance and higher evenness of lepidopterans in restored forests. The community composition of pollinators between the two forest types was similar. The taxonomic diversity of all pollinator taxa was positively related to canopy openness and flower diversity, while lepidopterans were also found to be sensitive to forest fragmentation at the landscape level. Comparing restored forests with natural reference systems suggested that the restoration of forests has the potential to support pollinators in degraded agricultural landscapes. Our results further provide valuable insights to guide forest ecological restoration targeting pollinators, in view of several ambitious conservation and restoration commitments undertaken at international level.